There are many methods for CBM gas reservoir evaluation, but the catastrophe theory is rarely used in such methods. Based on an analysis of the principles of the catastrophe theory, a multi-level hierarchy is established consisting of a target layer, a criteria layer and an index layer for the evaluation of CBM reservoirs by comprehensively considering A (resource characteristics), B (exploitation performance), C (reservoir characteristics), D (structural features). A catastrophe model was built for CBM reservoir evaluation. The index layers Al (gas content), A2 (resource abundance) and A3 (gas saturation) constitute a swallow tail catastrophe model; SI (reservoir permeability), B2 (reservoir pressure), B3 (porosity of the coal seam roof) and B4 (porosity of the coal seam floor) constitute a butterfly catastrophe model) CI (coal seamthickness), C2 (coal rank) and C3 (ash content) constitute a swallow tail catastrophe model; Dl (structural feature) and D2(hydrology characteristic) constitute a cusp catastrophic model. The criterion layers of A, B, C and D constitute a butterfly catastrophe model. The CBM reservoirs in the Shagou Coalfield of the Zhunnan mining area, southern Junggar Basin, were evaluated by using the catastrophe theory. It is believed that the coal seam M5 in the Middle-Lower Jurassic Badaowan Fm is the most favorable CBM reservoir, followed by coal seams M6, M8, M9 and M19. The results are in good agreement with that obtained by using the fuzzy mathematic method. Compared with other CBM gas reservoir evaluation methods, this method is much simpler and more reliable and can also minimize the influences of subjective factors.
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